The present disclosure relates to two coordinate measuring devices. One of these devices belongs to a class of instruments that measure the coordinates of a point by probing the point with an articulated mechanical structure. The probing may be performed with a mechanical probe tip or with a non-contact scanning device. The position of the probe tip is determined by the readings of angular encoders located at the mechanical joints that interconnect the articulating segments. This type of device, whether it uses a mechanical probe tip or a scanner, is referred to as an articulated-arm coordinate measuring machine (CMM). An exemplary system belonging to this class of devices is described by U.S. Pat. No. 5,402,582 to Raab.
The other of these devices is an instrument, referred to as a laser tracker, which measures the coordinates of a point by sending a laser beam to a retroreflector target that is in contact with the point. The laser tracker determines the coordinates of the point by measuring the distance and the two angles to the retroreflector. The distance is measured with a distance-measuring device such as an absolute distance meter or an interferometer. The angles are measured with an angle-measuring device such as an angular encoder. A gimbaled beam-steering mechanism within the instrument directs the laser beam to the point of interest. Exemplary systems belonging to this class of instruments are described by U.S. Pat. No. 4,790,651 to Brown et al. and U.S. Pat. No. 4,714,339 to Lau et al.
The articulated-arm CMM is capable of being bent into a variety of orientations. Because of this, it is able to measure “hidden” points; that is, points that are hidden from the line-of-sight view of a measuring device such as a laser tracker. On the other hand, the laser tracker can measure over a much larger volume than the articulated-arm CMM. What is needed is a way to obtain the convenience of measuring hidden points with the articulated-arm CMM over the larger measurement volume of the laser tracker.